Implantable medical devices (IMDs) may be configured to provide therapy to and/or sense physiological parameters of an individual in which the IMD is implanted. As one example, an IMD may be configured to provide pacing and/or defibrillation signals to the heart. Additionally or alternatively, an IMD may be configured to sense electrical signals attendant to depolarization and repolarization of the heart.
To provide electrical stimulation therapy and to sense electrical signals, the IMD may be coupled to one or more leads, each of which may include one or more electrodes. Typically, each of the electrodes is coupled to the IMD via a respective conductor within the lead. To sense other physiological parameters, an IMD may be coupled to one or more other sensors, such an accelerometer, a strain gauge, a pressure sensitive-capacitor, an optical perfusion sensor, an oxygen saturation sensor, an ultrasonic flow sensor, a thermistor, or an antimony electrode. In some cases, an IMD is coupled to such a sensor by a lead that also carries one or more electrodes, e.g., via two or more conductors within the lead. Furthermore, in order to reduce the number of conductors traversing the full length of a lead, it has been proposed to include one or more switching devices at relatively distal locations on the lead, the switching device or devices selectively couple two or more conductors of the lead to a greater number of electrodes.
Sensors and switching devices are examples of lead-borne devices, referred to herein as “satellites,” that communicate with an IMD to which the satellite is connected by a lead. For example, an IMD may transmit a signal to “wake-up” the satellite. For sensors, the IMD may transmit a command to cause the satellite to perform a measurement, and receive the measurement from the satellite. For switching devices, the IMD may provide a command that selects which electrodes are to be coupled to the IMD for delivery of electrical stimulation or sensing.